1. Field of the Invention
This invention relates to a method and an apparatus for receiving a synchronizing signal from means for controlling a television camera and converting the received synchronizing signal into a new synchronizing signal.
2. Description of the Prior Act
In a television monitoring system, as one of information transmission systems, at least one television monitor is switchably connected to a plurality of television cameras through a plurality of transmission lines. Therefore, the picture image from the television camera selected by the switching operation appears on the television monitor.
In such an information transmission system, it is necessary to synchronize the horizontal scanning and/or the vertical scanning of a plurality of television cameras in order to prevent the picture image on the monitor from being disturbed during and immediately after the selection and switching operation from one television camera to another.
As one of known devices for synchronizing a plurality of television cameras, there is an apparatus for transmitting synchronizing signals (which will be hereinafter referred to as a reference synchronizing signal) from control means, such as a controller, to the television cameras, and synchronizing the horizontal and vertical scannings of the television cameras with the transmitted reference synchronizing signals.
As the reference synchronizing signal in such a synchronizing apparatus, use is made of a vertical drive signal, a combination of the vertical drive signal and a horizontal drive signal, a vertical synchronizing signal, a composite synchronizing signal including the vertical synchronizing signal and a horizontal synchronizing signal, or a frame synchronizing signal having a level higher that the white level of a composite video signal and generated within the period of time corresponding to the vertical blanking interval in the composite video signal.
Since the reference synchronizing signals to be used are different, the reference synchronizing signal transmission methods are different, the apparatuses of this kind are respectively constructed different systems, depending on the reference synchronizing signals to be used, and are available in markets. Therefore, the instruments to be used are not interchangeable.